“All personnel have been accounted for and no one was injured,” said TVA spokesman Scott Brooks.

He said a concrete and steel coal storage silo at the Cumberland Fossil Plant collapsed inside a “powerhouse” for Unit 2, spilling coal into an adjacent area but no employees or major equipment were affected.

Unit 2 was off-line at the time the silo failed so there was no interuption of power generation. Brooks said it is a structure that is inspected regularly.

"Cumberland plant emergency personnel responded immediately," he said. "The area is cordoned off and an investigation is underway. We will provide more information as we have it. TVA Safety personnel and TVA Police are onsite."

Brooks said late Friday afternoon it was still too early to know what went wrong.

"Our first priority is to make sure the structure is stabilized so the investigation can continue," he said. "We will do a thorough investigation, no matter how long it takes."

Coal is stored in the silo until it is pulverized for burning in an eight-story furnace that creates steam to turn huge turbines. Combined, the two units at the plant, the largest coal-fire plant in TVA's fleet, are capable of generating 2,600 megawatts of electricity.

Annually it generates 18 billion kilowatt-hours of electricity, enough to power about 1.2 million homes.

Mark Hicks can be reached at 931-212-7626 or on Twitter: @markhicksleaf.